Doctors examined 32 studies involving 600,000 women, including 22,000 who had breast cancer.
After considering established risk factors such as age and late menopause, the researchers found a strong association with birth size, birth length and head circumference. Of the three, birth length showed the strongest link.
The study showed that women who weighed nine pounds or more at birth had a 12 percent higher chance of breast cancer than babies weighing 6 to 7 pounds.